1. During the first six days of cephalic regeneration of Eisenia foetida several successive metabolic stages have been found as follows: a first and short stimulation of protein synthesis (from the 6th to the 16th hour), a first and short stimulation of RNA synthesis (from the 12th to the 36th hour), a second stimulation of protein synthesis, larger than the first and continuous (beginning at the 16th hour), a second, long and continuous stimulation of RNA synthesis (beginning at the 48th hour) and finally the S phase. 2. The regeneration is totally stopped by the RNA synthesis inhibitors (actinomycin D and 5-fluorouracil) when added during the first RNA stimulation (0-36 hours). If added after the 36th hour the same inhibitors give mostly delay or anomalies in regeneration. Same results are obtained when animals are treated during 48 hours before operation. 3. The use of protein synthesis inhibitors (puromycin and cycloheximide) for short times does not stop regeneration, but gives anomalies and long delays in regeneration. 4. An urea soluble fraction (and specially proteins with smaller molecular weight) is preferentially synthesized during the first stimulation of protein synthesis. It is postulated that these proteins are characteristic of the early phase of cellular activation. 5. The RNA synthesized during the first three days is polydispersed. The RNAs formed at 0, 24, 48 and 72 hours are mostly of ribosomal and transfer type. Nevertheless an increased synthesis of the heaviest fractions and those between 18 S and 4-5 S peaks, occurs at the 16th hour (beginning of the first RNA synthesis stimulation). An increased production of heavy RNA is also noticed at 36 hours before the beginning of the second RNA synthesis stimulation.